Site Characterization of the Northern Site of the Cherenkov Telescope Array

Gaug, M.; Font, L.; Maggio, C.

doi:10.1051/epjconf/201714401010

Cited by 7 publications

(9 citation statements)

References 27 publications

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“…1958). The GDAS data are provided for a grid of integer latitude and longitude (in degrees), hence the closest grid point for the MAGIC telescope corresponds to 29 • N and 18 • W. The GDAS predictions have been ground-validated with the MAGIC weather station resulting in excellent agreement of the predicted pressure values and a small positive bias of two degrees for the temperatures (Gaug et al 2017), attributed to local ground cooling effects at night, which is not reproduced at the GDAS grid point, located over the Sea. A more accurate local modelling of the molecular profile involving the Weather Research and Forecasting (WRF) 2 is currently investigated, but out of the scope of this article.…”

Section: Subtraction Of the Molecular Profilementioning

confidence: 99%

Characterizing the aerosol atmosphere above the Observatorio del Roque de los Muchachos by analyzing seven years of data taken with an GaAsP HPD-readout, absolutely calibrated elastic LIDAR

Fruck,

Gaug,

Hahn

et al. 2022

Preprint

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We present a new elastic LIDAR concept, based on a bi-axially mounted Nd:YAG laser and a telescope with HPD readout, combined with fast FADC signal digitization and offline pulse analysis. The LIDAR return signals have been extensively quality checked and absolutely calibrated. We analyze seven years of quasi-continuous LIDAR data taken during those nights when the MAGIC telescopes were operating. Characterization of the nocturnal ground layer yields zenith and azimuth angle dependent aerosol extinction scale heights for clear nights. We derive aerosol transmission statistics for light emitted from various altitudes throughout the year and separated by seasons. We find further seasonal dependencies of cloud base and top altitudes, but none for the LIDAR ratios of clouds. Finally, the night sky background light is characterized using the LIDAR photon backgrounds.

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Section: Subtraction Of the Molecular Profilementioning

confidence: 99%

Characterizing the aerosol atmosphere above the Observatorio del Roque de los Muchachos by analyzing seven years of data taken with an GaAsP HPD-readout, absolutely calibrated elastic LIDAR

Fruck,

Gaug,

Hahn

et al. 2022

Preprint

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“…to assess the range of variation of t µ,mol due to changes in the atmospheric profile for the LST, we used the data of one full year from the "Global Data Assimilation System" (GDAS) "Final Analysis" database 16 for the closest grid point to La Palma, whose temperature and pressure predictions show excellent correlation with the measurements of the MAGIC weather station (Gaug et al 2017), apart from a constant 2 • C bias, which can be corrected. The full height-resolved temperature and pressure profiles were used to derive B µ for fixed telescope efficiencies ξ det ( ) for the LST.…”

Section: Atmospheric Transmissionmentioning

confidence: 99%

“…The MAGIC Collaboration has found that the altitude profile of the aerosol extinction coefficient for clear nights is exponential with a scale height of H aer ≈(500-700) m (Gaug et al 2017), with an aerosol optical depth (AOD) on the ground of about (AOD≈ 0.02) on average, however ranging from practically zero to almost 0.1 for normal clear nights.…”

Section: Aerosol Transmission -mentioning

confidence: 99%

Using Muon Rings for the Calibration of the Cherenkov Telescope Array: A Systematic Review of the Method and Its Potential Accuracy

Gaug

Mitchell

Maccarone

et al. 2019

ApJS

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The analysis of ring images produced by muons in an Imaging Atmospheric Cherenkov Telescope (IACT) provides a powerful and precise method to calibrate the IACT optical throughput and monitor its optical point-spread function (PSF). First proposed by the Whipple collaboration in the early 90's, this method has been refined by the so-called second generation of IACT experiments: H.E.S.S., MAGIC and VERITAS. We review here the progress made with these instruments and investigate the applicability of the method as the primary throughput calibration method for the different telescope types forming the future Cherenkov Telescope Array (CTA). We find several additional systematic effects not yet taken into account by previous authors and propose several new analytical methods to include these in the analysis. Slight modifications in hardware and analysis need to be made to ensure that such a calibration works as accurately as required for the CTA. We derive analytic estimates for the expected muon data rates for optical throughput calibration, camera pixel flat-fielding and monitoring of the optical PSF. The achievable statistical and systematic uncertainties of the method are also assessed.

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“…The scattering probability becomes radially symmetric in such a case. To estimate the dependency of N (h)/Ns on altitude, we use a typical atmospheric winter condition at the ORM 8 (Gaug et al 2017) with: Aerosols scatter light more efficiently than molecules and usually less isotropically, due to their larger sizes, although they are much less in number density. World-class astronomical observatories are however characterized by extremely low aerosol contamination on average.…”

Section: Scattering Of the Laser Light In The Lower Atmospherementioning

confidence: 99%

“…World-class astronomical observatories are however characterized by extremely low aerosol contamination on average. For instance, typical winter nights on La Palma show aerosol optical thicknesses (AOTs) of the ground layer of the order of only 0.02 at λ = 532 nm, with extinction coefficients distributed exponentially with a scale height of around Haer ≈ 500 m (Gaug et al 2017), hence:…”

Section: Scattering Of the Laser Light In The Lower Atmospherementioning

confidence: 99%

Impact of Laser Guide Star facilities on neighbouring telescopes: the case of GTC, TMT, VLT, and ELT lasers and the Cherenkov Telescope Array

Gaug

Doro

2018

Monthly Notices of the Royal Astronomical Society

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Powerful Laser Guide Star (LGS) systems are standard for the next-generation of extremely large telescopes. However, modern earth-based astronomy has gone through a process of concentration on few sites with exceptional sky quality, resulting in those becoming more and more crowded. The future LGS systems encounter hence an environment of surrounding astronomical installations, some of which observing with large fields-of-view. We derive formulae to calculate the impact of LGS light on the camera of a neighbouring telescope and the probabilities for a laser crossing the camera field-of-view to occur, and apply these to the specific case of the next very-high-energy gamma-ray observatory "Cherenkov Telescope Array" (CTA). Its southern part shall be constructed in a valley of the Cerro Armazones, Chile, close to the "Very Large Telescope" (VLT) and the "European Extremely Large Telescope" (ELT), while its northern part will be located at the "Observatorio del Roque de los Muchachos", on the Canary Island of La Palma, which also hosts the "Gran Telescopio de Canarias" (GTC) and serves as an optional site for the "Thirty Meter Telescope" (TMT), both employing LGS systems. Although finding the artificial star in the field-of-view of a CTA telescope will not disturb observations considerably, the laser beam crossing the field-of-view of a CTA telescope may be critical. We find no conflict expected for the ELT lasers, however, 1% (3%) of extra-galactic and 1% (5%) of galactic observations with the CTA may be affected by the GTC (TMT) LGS lasers, unless an enhanced version of a laser tracking control system gets implemented.creation of several guide stars is also possible, to achieve asterism with a radial distance from science target ranging from 0.5 to 6 on the sky. The LGS will likely be operated regularly during observations, and their scattered light (Rayleigh and Mie) will then be seen by other telescopes until distances of several kilometers from the location of their host observatory. Assuming the close-by installation observes in a wavelength range enclosing that of the LGS lasers, the scattered laser light may then leave spurious light tracks on the cameras and affect operation in several ways: a) by generating false triggers (for installations which trigger image readout e.g. from Cherenkov light pulses) the star guider camera and the precision pointing of the telescopes, and ultimately, d) by affecting the duty cycle, if active laser avoidance is chosen. Several of the enumerated problems can be often overcome with the use of Notch-filters (Schallenberg et al. 2010) or band-pass filters (Ahnen et al. 2017;Archambault et al. 2017), however this is not always possible at a reasonable cost, particularly not in the case of the CTA, where every camera pixel would need to be covered by such a filter. Light losses at smaller wavelengths, particularly in the sensitive region from 300 nm to 500 nm need to be strictly controlled in order to ensure that sensitivity losses remain acceptable, particularly around the energ...

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Site Characterization of the Northern Site of the Cherenkov Telescope Array

Abstract: Abstract. We present the current knowledge and activities to assess the climatology of the "Observatorio del Roque de los Muchachos" (ORM), selected to host the Northern observatory of the CTA, with particular emphasis on molecular density profiles and aerosol extinction.

Cited by 7 publications

References 27 publications

Characterizing the aerosol atmosphere above the Observatorio del Roque de los Muchachos by analyzing seven years of data taken with an GaAsP HPD-readout, absolutely calibrated elastic LIDAR

Characterizing the aerosol atmosphere above the Observatorio del Roque de los Muchachos by analyzing seven years of data taken with an GaAsP HPD-readout, absolutely calibrated elastic LIDAR

Using Muon Rings for the Calibration of the Cherenkov Telescope Array: A Systematic Review of the Method and Its Potential Accuracy

Impact of Laser Guide Star facilities on neighbouring telescopes: the case of GTC, TMT, VLT, and ELT lasers and the Cherenkov Telescope Array

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